Technical Field
[0001] The present invention relates to detection of pressure signals, and more specifically
relates to a detection circuit and method that differentiate input signals, comprehend
the signal characteristics based on the results, and then segment and output only
an input signal from which a heat input signal (pyro signal) has been removed, so
as to detect only pressure input signals (piezo signals) from among input signals
supplied to a piezoelectric material.
Background Art
[0002] Piezoelectric materials generate a relatively large force compared with their own
weights and have a characteristic of quickly responding to a supplied voltage. With
such characteristics, piezoelectric materials are applied to various industries. There
are various components using these piezoelectric materials (in other words, the form
of the piezoelectric material) . Among them, a piezoelectric film is a material that
is displaced when force is applied to both its ends, and a voltage is generated in
proportion to the displacement. With such characteristics, piezoelectric films are
widely used in piezoelectric generators, sensors, ultrasonic transmitters and receivers,
and the like.
[0003] Fig. 1a is a diagram showing a piezoelectric film, Fig. 1b is a diagram showing the
front end of a pressure sensor, and Fig. 1c is a diagram showing an output voltage
signal according to input impedance R.
[0004] Referring to Fig. 1a to Fig. 1c, pressure sensing using a piezoelectric element is
performed by discharging or integrating the charge generated in a piezoelectric film
using an impedance adapter or a Miller's integrator in the front end. Among them,
the impedance adapter has a characteristic that the output waveform changes according
to input impedance R. Then, by integrating the output voltage signal corresponding
to the input impedance R, signal information measured by the sensor can be obtained.
However, the final signal information thus obtained includes input information of
both pressure and heat. Previously, only physical pressure was measured without a
pressure signal due to heat, or a method of absorbing heat using a specific substance
to thereby reduce the influence of heat was used. However, these techniques are limited
in that the heat input signals cannot be completely eliminated.
[0005] Fig. 2a is a graph showing the characteristics of a piezoelectric element on a temperature
basis, and Fig. 2b is a graph showing the characteristics of a piezoelectric element
on humidity basis. Fig. 3a is a diagram showing a pressure input signal from which
a heat input signal is removed, and Fig. 3b is a diagram showing both a heat input
signal and a pressure input signal.
[0006] Pressure sensing is used mainly for touch sensing through a human finger; at this
time, input information due to heat is also displayed because of a temperature difference
between the finger and the piezoelectric element.
[0007] Figs. 3a and 3b show more specific characteristics of the pressure input signal and
the heat input signal. Referring to Fig. 3a, the pressure input signal has characteristics
that an input signal upon touching (touch down (pressing)) is output as a positive
value, and an input signal upon release (touch up (releasing)) is output as a negative
value. Referring to Fig. 3b, there is a difference in output speed between the pressure
input signal and the heat input signal. This is because the conduction speed of the
temperature input signal is relatively longer (slower) than the conduction speed of
the pressure input signal.
Citation List
Patent Documents
Summary of Invention
Technical Problem
[0009] Therefore, the present invention was proposed in consideration of the various conditions
as described above, and an object of the present invention to remove the heat input
signal by using the difference in the speed of supplying the pressure input signal
and the heat input signal and the differential information, thereby outputting only
the pressure input signal.
[0010] An object of the present invention is to significantly reduce the influence on the
thermal reaction as compared with the prior art, and to increase the reaction speed
of the input terminal at the front end, thereby enabling detection of a pressure signal
at a higher speed.
[0011] Another object of the present invention is to output a signal having a superior thermal
reaction attenuation effect compared with the use of an additional process for heat
absorption when a piezoelectric material is produced.
[0012] The objects of the present invention are not limited to those mentioned above, and
unmentioned or other objects would clearly be understood by those skilled in the art
from the following descriptions.
Solution to Problem
[0013] As described above, examples of a component using a piezoelectric material (in other
words, the form of the piezoelectric material) include a piezoelectric film.
The present invention regarding piezoelectric film is explained in detail below. Based
on common technical knowledge, the description below also applies to components or
forms other than a piezoelectric film.
[0014] In order to achieve the above objects, the pressure signal detection circuit in which
a pyroelectric signal from a piezoelectric film is suppressed according to the technical
idea of the present invention is constituted of a signal processing unit for receiving
input of an input signal from a piezoelectric film, a differentiator for differentiating
the input signal for the analysis of the signal component of the input signal, a signal
processing unit for outputting an analysis value of the signal component of the input
signal based on the differential value of the differentiator, an offset removal unit
for removing offset of the input signal using the signal component analysis value,
and an integrating unit for integrating the input signal to output a pressure input
signal value in which a heat input signal value is deleted.
[0015] The pressure signal detection circuit is characterized by further comprising a filter
unit constituted of a low-pass filter (LPF) and a moving average filter (MAF) for
removing noise of the input signal supplied from the signal input unit.
[0016] The signal processing unit is characterized by comparing the differentiated input
signal value with a preset threshold value to determine whether the input signal is
a pressure input signal or a heat input signal. When the differentiated input signal
value is equal to or greater than the preset threshold value, the input signal is
determined to be a pressure input signal and the integrating unit is executed. When
the differentiated input signal value is smaller than the preset threshold value,
the input signal is determined to be a heat input signal, and the offset removal unit
is executed.
[0017] When a pressure input signal during the reference time is not re-detected after the
pressure input signal is detected from the differentiated input signal value, the
signal processing unit outputs a reset signal for initializing the integrating unit.
[0018] When the pressure input signal is not detected from the differentiated input signal
value in all sections, the signal processing unit outputs a reset signal for initializing
the integrating unit.
[0019] The offset removal unit outputs a value obtained by subtracting the heat input signal
from the input signal.
[0020] In order to achieve the object described above, the pressure signal detection method
in which a pyroelectric signal from a piezoelectric film is suppressed according to
the technical idea of the present invention is characterized by comprising a signal
input step of receiving input of an input signal from a piezoelectric film from a
signal processing unit, a differentiating step of differentiating the input signal
for the analysis of the signal component of the input signal by an differentiator,
a signal processing step of outputting a signal component analysis value of the input
signal based on the differential value of the differentiator in a signal processing
unit, an offset removal step of removing offset of the input signal using the signal
component analysis value of the signal processing unit, and an integrating step of
integrating the input signal in the integrating unit to output a pressure input signal
value in which a heat input signal value is deleted.
[0021] The pressure signal detection method is characterized by further comprising a filter
step of removing noise of the input signal in a filter unit so as to remove noise
from the input signal supplied from the signal input step.
[0022] The signal processing step is characterized by comparing the differentiated input
signal value with a preset threshold value to determine whether the input signal is
a pressure input signal or a heat input signal. If the value of the differentiated
input step is equal to or greater than the predetermined threshold value, the input
signal is determined to be a pressure input signal and the integrating step is executed.
If the differentiated input signal value is smaller than the predetermined threshold
value, the input signal is determined to be a heat input signal, and the offset removal
step is executed.
[0023] When a pressure input signal during the reference time is not re-detected after the
pressure input signal is detected from the differentiated input signal value, the
signal processing step outputs a reset signal for initializing the integrating unit
(integrating step).
[0024] When the pressure input signal is not detected from the differentiated input signal
value in all sections, the signal processing step outputs a reset signal for initializing
the integrating unit (integrating step).
[0025] The offset removal step outputs a value obtained by subtracting the heat input signal
from the input signal.
Advantageous Effects of Invention
[0026] The following is achieved with the above circuit and the method for detecting a pressure
signal in which a pyroelectric signal is suppressed in the piezoelectric film.
[0027] First, an effect of outputting only pressure input signals is ensured by removing
a heat input signal using a difference in input speed between the pressure input signal
and the heat input signal, as well as differential information.
[0028] Second, an effect of significantly reducing the influence on the thermal reaction
as compared with the prior art, increasing the reaction speed of the input terminal
at the front end, thereby enabling detection of a pressure signal at a higher speed,
is ensured.
[0029] Third, an effect of outputting a signal with a superior thermal reaction attenuation
effect compared with the use of an additional process for heat absorption when a piezoelectric
film is produced is ensured.
Brief Description of Drawings
[0030]
Fig. 1a is a drawing showing a piezoelectric film.
Fig. 1b is a drawing showing the front end of a pressure sensor.
Fig. 1c is a diagram showing an output voltage signal corresponding to input impedance
R.
Fig. 2a is a graph showing the characteristics of a piezoelectric element on temperature
basis.
Fig. 2b is a graph showing the characteristics of a piezoelectric element on humidity
basis.
Fig. 3a is a diagram showing a pressure input signal from which a heat input signal
is removed.
Fig. 3b is a diagram showing a heat input signal together with a pressure input signal.
Fig. 4 is a block diagram showing a pressure signal detection circuit in which a pyroelectric
signal is suppressed in a piezoelectric film as an embodiment of the present invention.
Fig. 5a is a graph showing a pressure input signal by Touch_Input in Fig. 4.
Fig. 5b is a graph showing a heat input signal by Touch_Input in Fig. 4.
Fig. 6 is a graph showing a pressure input signal by Rest _Period in Fig. 4.
Fig. 7a is a graph showing a pressure input signal by Touch-OFF in Fig. 4.
Fig. 7b is a graph showing a heat input signal by Touch-OFF in Fig. 4.
Fig. 8 is a drawing showing operation of the entire system using a pressure input
signal as an embodiment of the present invention.
Fig. 9 is a drawing showing operation of the entire system using a heat input signal
as an embodiment of the present invention.
Fig. 10 is a diagram showing a Simulink-implemented digital system using an ADC conversion
input as an embodiment of the present invention.
Fig. 11a is a drawing showing a system in which an analog amplifier and a filter circuit
are added to a piezoelectric film input unit, as an embodiment of the present invention.
Fig. 11b is a drawing showing a system in which an analog amplifier and a filter circuit
are added to a piezoelectric film input unit, as an embodiment of the present invention.
Fig. 12 is a flow chart showing a pressure signal detection method in which a pyroelectric
signal is suppressed in a piezoelectric film as an embodiment of the present invention.
Fig. 13a is a drawing showing changes in the output signal of a piezoelectric element
according to the temperature environment.
Fig. 13b is a drawing showing changes in the output signal of a piezoelectric element
according to a severe temperature environment, as an embodiment of the present invention.
Description of Embodiments
[0031] For a full understanding of the invention and its operational advantages and the
objects achieved by the practice of the invention, reference should be made to the
accompanying drawings illustrating the preferred embodiments of the invention and
the content described in the accompanying drawings. The characteristics and the advantages
of the present invention will be clarified by the following detailed description based
on the accompanying drawings. In advance, it should be noted that the terms and words
used in this specification and the claims are based on the principle by which the
inventors can properly define the concept of the term in order to best describe their
invention. Therefore, a term or a word should be construed as a meaning and a concept
consistent with the technical idea of the present invention. In addition, it should
be noted that a specific description of known functions related to the present invention
and specific explanations of those functions is omitted when the gist of the present
invention can be made unnecessarily vague.
[0032] In the present invention, the piezoelectric material is a pyroelectric piezoelectric
material and may also be referred to as a "pyroelectric material." The piezoelectric
material may be a ferroelectric. In this embodiment, the piezoelectric material is,
but is not limited to, a piezoelectric film. Fig. 4 is a block diagram showing a pressure
signal detection circuit in which a pyroelectric signal is suppressed in a piezoelectric
film, as an embodiment of the present invention. As shown in Fig. 4, the pressure
signal detection circuit in which a pyroelectric signal in a piezoelectric film is
suppressed comprises a signal input unit (100) that is constituted of a piezoelectric
film and an amplifier and receives input of an input signal from the piezoelectric
film, a differentiator (300) for differentiating the input signal for the analysis
of the signal component of the input signal, a signal processing unit (400) for outputting
an analysis value of the signal component of the input signal based on the differential
value of the differentiator (300), an offset removal unit (500) for removing offset
of the input signal using the signal component analysis value, and an integrating
unit (600) for integrating the input signal to output a pressure input signal value
from which a heat input signal value is removed. The pressure signal detection circuit
further comprises a filter unit (200) constituted of a low-pass filter (LPF) and a
moving average filter (MAF) for removing noise of the input signal supplied from the
signal input unit (100). At this point, the filter unit (200) removes 50/60 Hz power
noise from the input signal.
[0033] The signal processing unit (400) compares the differentiated input signal value with
a preset threshold value, and segments the input signal as a pressure input signal
or a heat input signal. If the differentiated input signal value is equal to or greater
than the preset threshold value, the input signal is determined to be a pressure input
signal and the integrating unit is executed. If the differentiated input signal value
is smaller than the predetermined threshold value, the input signal is determined
to be a heat input signal, and the offset removal unit is executed.
[0034] Further, when a pressure input signal during the reference time is not re-detected
after a pressure input signal is detected from the differentiated input signal value,
the signal processing unit (400) outputs a reset signal for initializing the integrating
unit (600). When a pressure input signal is not detected from the differentiated input
signal value in all sections, the signal processing unit (400) outputs a reset signal
for initializing the integrating unit (600).
[0035] The offset removal unit (500) outputs a value obtained by subtracting the heat input
signal from the input signal mentioned above.
[0036] Fig. 5a to Fig. 7b are drawings for specifically explaining the signal processing
unit (400) of Fig. 4. Figs. 5a and 5b are graphs showing a pressure input signal and
heat input signal by Touch_Input in Fig. 4. (In the present invention, although the
preset threshold value is 100, the value can be easily changed based on the differential
value of the heat input signal.) Fig. 6 is a graph showing a pressure input signal
by Rest_Period in Fig. 4. Fig. 7a and 7b are graphs showing a pressure input signal
and a heat input signal by Touch_OFF in Fig. 4.
[0037] First, Touch Input in the signal processing unit (400) shown in Fig. 4 determines
whether the signal is a pressure input signal or a heat input signal by using information
of the differentiated input signal. The differential value of the worst heat input
signal is smaller than the differential value of the pressure input signal. The graph
specifically showing this is the same as Fig. 5b.
[0038] In the cases shown in Figs. 5a and 5b, an input signal (Input), a Balance_Ref signal
(MAF_LPF), and a differentiated input signal (Diff) are included as the pressure input
signal and the heat input signal. Referring to Fig. 5a, in the pressure input signal
(Input), a large differentiated input signal (Diff) is output due to the conduction
speed being relatively faster than that of the heat input signal (Input). At this
point, it is possible to output an accurate section (shown with red arrows) in which
the pressure input signal is supplied from the differentiated input signal (Diff).
[0039] On the other hand, referring to Fig. 5b, a comparison between the pressure input
signal (Input) and the heat input signal (Input) reveals that the heat input signal
(Input) reacts more smoothly than the pressure input signal (Input) due to the conduction
speed of the temperature input signal. Accordingly, the signal obtained by differentiating
the heat input signal (Input) is output as a small value (Diff). The differentiated
input signal (Diff) does not exceed 100, which is the value of the preset threshold
value. This degree of a threshold value is larger than the differentiated input signal
even in the presence of the maximum heat change; however, the threshold value may
be easily changed according to the surrounding environment.
[0040] Rest_Period in the signal processing unit (400) of Fig. 4 determines whether a pressure
input signal during the reference time is re-detected after a pressure input signal
is detected from the differentiated input signal value. The graph specifically showing
this operation is the same as Fig. 6.
[0041] In the case shown in Fig. 6, an input signal (Input), a Balance_Ref signal (MAF_LPF),
and a differentiated input signal (Diff) are included as the pressure input signal.
[0042] As shown in Fig. 6, if a pressure input signal is not re-detected for a certain period
of time (see the part shown with a blue dotted arrow) from the differentiated input
signal (Diff), the signal processing unit (400) outputs a reset signal for initializing
the integrating unit (600).
[0043] Touch _OFF in the signal processing unit (400) of Fig. 4 determines whether or not
a pressure input signal is detected from the differentiated input signal value (Diff)
in all sections. The presence or absence of the detection is determined based on a
circumstance in which the differentiated input signal value (Diff) becomes a large
negative value.
[0044] When the circumstance in which the value of the differential input signal (Diff)
becomes a large negative value (shown with a red arrow and line) is displayed as shown
in Fig. 7a, the signal processing unit (400) outputs a reset signal for initializing
the integrating unit (600).
[0045] Fig. 7b shows that, in this case, a pressure input signal is not detected as a heat
input signal in all sections.
[0046] Fig. 8 is a drawing showing the operation of the entire system using a pressure input
signal as an embodiment of the present invention, and Fig. 9 is a drawing showing
the operation of the entire system using a heat input signal as an embodiment of the
present invention. As shown in Figs. 8 and 9, the input signal (Input) is first supplied
to the signal input unit (100) as a signal from the piezoelectric film, and then transmitted
to the filter unit (200). Noise is removed from the transmitted input signal (Input)
by the filter unit (200) constituted of a low-pass filter (LPF) and a moving average
filter (MAF) . The signal output at this point is a Balance Ref signal (MAF_LPF).
The Balance_Ref signal (MAF_LPF) is supplied to the differentiator (300) to be differentiated.
The signal output at this point is the differentiated input signal (Diff). The differentiated
input signal (Diff) is transmitted to Touch _Input, and Touch _Input determines whether
the signal thus transmitted is a heat input signal or a pressure input signal.
[0047] As shown in Fig. 8, Balance_Ref. serves to fix the input signal when the differentiated
input signal (Diff) is determined to be a pressure input signal. Conversely, as shown
in Fig. 9, when the differentiated input signal (Diff) is determined to be a heat
input signal, the input signal thus determined as a heat input signal is removed as
being regarded as a meaningless signal by the offset removal unit (500) (determination
as to whether to execute the offset removal unit (500) is performed using the input
signal thus determined) . When a pressure input signal is not detected, the input
signal (Input) and the Balance_Ref signal (MAF_LPF) have the same value. When a pressure
input signal is detected from the differentiated input signal (Diff), Balance_Ref.
detects only an accurate input section where a pressure input signal is supplied.
Balance_Ref. (MAF_LPF) holds only the signal immediately before the detection of the
pressure input signal. At this point, the process of removing the meaningless signal
is performed as a process of outputting 0, which is a value obtained by subtracting
the heat input signal output from Touch-Input from the input signal output from the
filter unit (200) . In the above removal process, various signals other than the pressure
input signal, including a heat input signal, are removed. As a result, the signal
output from the offset removal unit (500) is neatly (clearly) output by the offset
removal unit (500). In Fig. 9, the signal output from the offset removal unit (500)
is 0.
[0048] As shown in Fig. 8, the integrating unit (600) is provided so as to output the process
of input signal transmission; the integrating unit (600) integrates the input signal
to restore a pressure input signal. This is because, although the presence or absence
of pressure application by the pressure signal detection from the piezoelectric film
is perceivable, the process of applying a pressure is not perceivable.
[0049] Fig. 10 is a drawing showing a Simulink-implemented digital system using ADC conversion
input, as an embodiment of the present invention. Figs. 11a to 11b are drawings showing
a system in which an analog amplifier and a filter circuit are added to a piezoelectric
film input unit, as an example of the present invention. The filter unit (200), the
differentiator (300), and the integrating unit (600) shown in Fig. 10 can be implemented
with digital and analog circuits. The signal processing unit (400) can be implemented
with an analog circuit or a microprocessor, and the microprocessor's memory may also
be used. At this point, the memory recognizes the pressure input signal and stores
it in real time in order to store the input signal and analysis data of the signal
component of the input signal. Furthermore, a sensor for compensation according to
the temperature and humidity may be added to the signal processing unit (400).
[0050] As shown in Figs. 11a to 11b, this can be implemented with a circuit using a piezoelectric
film input unit amplifier. At this point, the analog amplifier can amplify a piezoelectric
signal to an appropriate signal level, and the filter circuit is used for noise removal.
[0051] Fig. 12 is a flow chart showing, as an embodiment of the present invention, a pressure
signal detection method in which a pyroelectric signal is suppressed in a piezoelectric
film. As shown in Fig. 12, the pressure signal detection method in which a pyroelectric
signal is suppressed in the piezoelectric film comprises a signal input step (S100)
for receiving input of an input signal from a piezoelectric film in a signal input
unit (100), a differentiating step (S300) for differentiating the input signal for
the analysis of the signal component of the input signal in a differentiator (300),
a signal processing step (S400) for outputting an analysis value of the signal component
of the input signal based on the differential value of the differentiator in a signal
processing unit (400), an offset removal step (S500) for removing offset of the input
signal using the signal component analysis value from the signal processing unit (400)
in an offset removal unit (500), an integrating step (S600) for integrating the input
signal to output a pressure input signal value from which a heat input signal value
is removed in an integrating unit (600) (at an integrating unit 600), and further
comprises a filter step (S200) for removing noise of the input signal from the filter
unit (200) so as to remove noise of the input signal supplied in the signal input
step (S100). At this point, the filter step (S200) removes 50/60 Hz power noise from
the input signal.
[0052] In the signal processing step (S400), the differentiated input signal value is compared
with a preset threshold value to determine whether the input signal is a pressure
input signal or a heat input signal. If the differentiated input signal value is equal
to or greater than the predetermined threshold value, the input signal is determined
to be a pressure input signal, and the integrating step (S600) is executed. If the
differentiated input signal value is smaller than the predetermined threshold value,
the input signal is determined to be a heat input signal, and the offset removal step
(S500) is executed.
[0053] Further, in the signal processing step (S400), when a pressure input signal during
the reference time is not re-detected after a pressure input signal is detected from
the differentiated input signal value, a reset signal for initializing the integrating
step (S600) (integrating unit (600)) is output. In the signal processing step (S400),
when a pressure input signal is not detected from the differentiated input signal
value in all sections, a reset signal for initializing the integrating step (S600)
(integrating unit (600)) is output.
[0054] In the offset removal step (S500), a value obtained by subtracting the heat input
signal from the input signal is output.
[0055] Fig. 13a is a drawing showing changes in output signal of a piezoelectric element
according to the temperature environment. Fig. 13b is a drawing showing changes in
the output signal of a piezoelectric element according to a severe temperature environment,
as an embodiment of the present invention. As shown in Fig. 13a, the output signal
of the piezoelectric element is affected not only by the pressure but also by the
environment due to heat (temperature) (the upper graph shows the output voltage of
the piezoelectric sensor when a constant pressure of 200 kPa is applied at -10°C for
150 seconds, and the lower graph shows the output voltage of the piezoelectric sensor
when a constant pressure of 200 kPa is applied at 50°C for 150 seconds).
[0056] On the other hand, as shown in Fig. 13b, the change in the output signal of the piezoelectric
element according to one embodiment of the present invention is not affected by the
change in the environment due to heat (temperature).
[0057] The pressure signal detection circuit of the present invention may be applied to
a piezoelectric film in which a heat absorbing substance is added, or a piezoelectric
film (bimorph piezoelectric film or the like) having a structure for attenuating pyroelectric
signals. In these applications, the SN ratio can be improved compared with the mode
in which the pressure signal detection circuit of the present invention is applied
to a normal piezoelectric film, and it therefore becomes possible to detect even weaker
pressures.
[0058] The material of the piezoelectric film is described below.
[0059] The piezoelectric film used in the present invention is preferably an organic pyroelectric
film, and more preferably an organic ferroelectric film.
[0060] As would usually be understood by a person skilled in the art, the "organic film,
" such as an organic piezoelectric film, organic pyroelectric film, or organic ferroelectric
film, is a film formed of an organic polymer (a polymer film) . As would be usually
understood by a person skilled in the art, the "organic piezoelectric film" is an
organic film having piezoelectricity. The organic pyroelectric film is an organic
film having pyroelectricity (and piezoelectricity) . The organic ferroelectric film
is an organic film having ferroelectricity (and pyroelectricity and piezoelectricity).
[0061] The organic film for constituting the organic pyroelectric film used in the present
invention is explained below.
[0062] Preferable examples of organic films include vinylidene fluoride-based polymer films,
odd-chain nylon films, and vinylidene cyanide-vinyl acetate copolymers.
[0063] The organic film used in the present invention is preferably a vinylidene fluoride-based
polymer film.
[0064] As would be usually understood by a person skilled in the art, the "vinylidene fluoride-based
polymer film" is a film constituted of a vinylidene fluoride-based polymer, and comprises
a vinylidene fluoride-based polymer.
[0065] In this specification, preferable examples of the vinylidene fluoride-based polymer
film include polyvinylidene fluoride films, vinylidene fluoride-tetrafluoroethylene
copolymer films, and vinylidene fluoride-trifluoroethylene copolymer films.
[0066] The terms "polyvinylidene fluoride films," "vinylidene fluoride-tetrafluoroethylene
copolymer films," and "vinylidene fluoride-trifluoroethylene copolymer films" used
in this specification are intended to include films comprising such a polymer as a
base material.
[0067] The polymer content of the organic film used in the present invention is preferably
50 mass% or more, more preferably 70 mass% or more, even more preferably 80 mass%
or more, still even more preferably 85 mass% or more, particularly 90 mass% or more,
and more particularly preferably 95 mass% or more. The upper limit of the content
is not particularly limited. For example, the upper limit may be 100 mass% or 99 mass%.
[0068] The "organic film" may optionally contain one or more components other than the polymer
as long as the effect of the present invention is not significantly impaired. Examples
of such other components include additives typically used in resin films.
[0069] Preferable examples of the polymer include vinylidene fluoride-based polymers.
[0070] Examples of "vinylidene fluoride-based polymer" include (1) a copolymer of vinylidene
fluoride and one or more monomers copolymerizable with vinylidene fluoride, and (2)
polyvinylidene fluoride.
[0071] Examples of the "monomers copolymerizable with vinylidene fluoride" in the" (1) copolymer
of vinylidene fluoride and one or more monomers copolymerizable with vinylidene fluoride"
include trifluoroethylene, tetrafluoroethylene, hexafluoropropylene, chlorotrifluoroethylene,
and vinyl fluoride.
The "one or more monomers copolymerizable with vinylidene fluoride" or at least one
of the monomers is preferably tetrafluoroethylene.
[0072] Preferred examples of the "vinylidene fluoride-based polymers" include a vinylidene
fluoride-tetrafluoroethylene copolymer.
[0073] The" (1) copolymer of vinylidene fluoride and one or more monomers copolymerizable
with vinylidene fluoride" preferably contains 5 mol% or more, 10 mol% or more, 15
mol% or more, 20 mol% or more, 25 mol% or more, 30 mol% or more, 35 mol% or more,
40 mol% or more, 45 mol% or more, 50 mol% or more, or 60 mol% or more, of repeating
units derived from vinylidene fluoride.
[0074] The molar ratio of the repeating units derived from tetrafluoroethylene to the repeating
units derived from vinylidene fluoride in the "vinylidene fluoride-tetrafluoroethylene
copolymer" is preferably within the range of 5/95 to 90/10, more preferably 5/95 to
75/25, even more preferably 15/85 to 75/25, and still even more preferably 36/64 to
75/25.
[0075] The copolymer with a high content of vinylidene fluoride is preferable in terms of
excellent solvent solubility and excellent processability of the film.
[0076] The molar ratio of the repeating units derived from tetrafluoroethylene to the repeating
units derived from vinylidene fluoride in the vinylidene fluoride/tetrafluoroethylene
copolymer is preferably within the range of 5/95 to 37/63, more preferably 10/90 to
30/70, and still more preferably 5/85 to 25/75.
[0077] The copolymer with a higher tetrafluoroethylene content is preferable in terms of
excellent heat resistance of the film. The molar ratio of the repeating units derived
from tetrafluoroethylene to the repeating units derived from vinylidene fluoride in
the vinylidene fluoride-tetrafluoroethylene copolymer is preferably within the range
of 60/40 to 10/90, more preferably 50/50 to 25/75, and even more preferably 45/55
to 30/70.
[0078] The vinylidene fluoride-tetrafluoroethylene copolymer may contain repeating units
derived from a monomer other than vinylidene fluoride and tetrafluoroethylene insofar
as the properties of the present invention are not significantly impaired. The content
of such repeating units can be usually, for example, 20 mol% or less, 10 mol% or less,
5 mol% or less, or 1 mol% or less. Such monomers are not limited as long as they can
be copolymerized with a vinylidene fluoride monomer and/or a tetrafluoroethylene monomer.
Examples include:
- (1) HFO-1234yf (CF3CF=CH2), 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooct-1-ene (C6 olefin), fluoromonomers (e.g., vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoropropene
(HFP), 1-chloro-1-fluoro-ethylene (1,1-CFE), 1-chloro-2-fluoro-ethylene (1,2-CFE),
1-chloro-2,2-difluoroethylene (CDFE), chlorotrifluoroethylene (CTFE), trifluorovinyl
monomers, 1,1,2-trifluorobutene-4-bromo-1-butene, 1, 1, 2-trifluorobutene-4-silane-1-butene,
perfluoroalkyl vinyl ether, perfluoromethyl vinyl ether (PMVE), perfluoropropyl vinyl
ether (PPVE), perfluoroacrylate, 2,2,2-trifluoroethyl acrylate, and 2-(perfluorohexyl)ethyl
acrylate); and
- (2) hydrocarbon-based monomers (e.g., ethylene, propylene, maleic anhydride, vinyl
ether, vinyl ester, allyl glycidyl ether, acrylic acid-based monomers, methacrylic
acid based monomers, and vinyl acetate).
[0079] It would be understood by a person skilled in the art that the present invention
is not limited to the structure and effects illustrated and described in the preferred
examples described above for giving examples of the technical idea of the present
invention, and various modifications and alterations may be made without departing
from the scope of the technical idea. Accordingly, all of such appropriate modifications
and alterations are included in the scope of the present invention.
Industrial Applicability
[0080] The pressure signal detection circuit of the present invention is applicable to a
device comprising a piezoelectric material having pyroelectricity and a circuit for
processing output signals of the piezoelectric material. More specifically, a device
comprising a circuit for processing output signals of the piezoelectric material and
the pressure signal detection circuit of the present invention is also included in
the scope of the present invention. Examples of the devices include touch panels,
biosensors, vibration sensors, pressure sensors, and information terminal devices.
Reference Numerals
[0081]
100: Signal Input Unit
200: Filter Unit
300: Differentiator
400: Signal Processing Unit
500: Offset Removal Unit
600: Integrating Unit
1. A pressure signal detection circuit in which a pyroelectric signal obtained from a
piezoelectric material is suppressed.
2. The pressure signal detection circuit according to claim 1, comprising a removal unit
for removing a heat input signal from an input signal from the piezoelectric material.
3. The pressure signal detection circuit according to claim 2, wherein the removal unit
removes a heat input signal using a difference in input speed between a pressure input
signal and a heat input signal.
4. The pressure signal detection circuit according to claim 3, comprising a differentiator
for differentiating an input signal to analyze a signal component of the input signal
from the piezoelectric material.
5. The pressure signal detection circuit according to claim 4, comprising:
a signal input unit for receiving input of an input signal from the piezoelectric
material;
a differentiator for differentiating an input signal to analyze a signal component
of the input signal;
a signal processing unit for outputting a signal component analysis value of the input
signal based on the differential value of the differentiator;
an offset removal unit for removing offset of the input signal using the signal component
analysis value; and
an integrating unit for integrating the input signal to output a pressure input signal
value from which a heat input signal value is removed.
6. The pressure signal detection circuit according to any one of claims 1 to 5, further
comprising:
a filter unit constituted of a low pass filter (LPF) and a moving average filter (MAF)
for removing noise of the input signal supplied from the signal input unit.
7. The pressure signal detection circuit according to claim 4 or 5, wherein the signal
processing unit compares the differentiated input signal value with a preset threshold
value to determine whether the input signal is a pressure input signal or a heat input
signal.
8. The pressure signal detection circuit according to claim 7, wherein when the differentiated
input signal value is equal to or larger than the predetermined threshold value, the
input signal is determined to be a pressure input signal, and the integrating unit
is executed; and when the differentiated input signal value is smaller than the predetermined
threshold value, the input signal is determined to be a heat input signal, and the
offset removal unit is executed.
9. The pressure signal detection circuit according to claim 5, wherein, when a pressure
input signal during a reference time is not re-detected after a pressure input signal
is detected from the differentiated input signal value, the signal processing unit
outputs a reset signal for initializing the integrating unit.
10. The pressure signal detection circuit according to claim 5, wherein, when a pressure
input signal is not detected from the differentiated input signal value in all sections,
the signal processing unit outputs a reset signal for initializing the integrating
unit.
11. The pressure signal detection circuit according to claim 5, wherein the offset removal
unit outputs a precise pressure value that is obtained by subtracting the heat input
signal and a noise signal from the input signal.
12. The pressure signal detection circuit according to any one of claims 1 to 11, wherein
the piezoelectric material is a piezoelectric film.
13. A device comprising a piezoelectric material and the pressure signal detection circuit
according to any one of claims 1 to 12.
14. The device according to claim 13, wherein the device is a touch panel, a biosensor,
a vibration sensor, a pressure sensor, or an information terminal device.
15. A pressure signal detection method in which a pyroelectric signal obtained from a
piezoelectric material is suppressed.
16. The pressure signal detection method according to claim 15, comprising a removal unit
for removing a heat input signal from an input signal from the piezoelectric material.
17. The pressure signal detection method according to claim 16, wherein the removal unit
removes a heat input signal using a difference in conduction speed between a pressure
input signal and a heat input signal.
18. The pressure signal detection method according to claim 17, comprising a differentiator
for differentiating an input signal to analyze a signal component of the input signal
from the piezoelectric material.
19. The pressure signal detection method according to claim 18, comprising:
a signal input step of receiving input of an input signal from the piezoelectric material
in a signal input unit;
a differentiating step of differentiating an input signal to analyze a signal component
of the input signal in a differentiator;
a signal processing step of outputting a signal component analysis value of the input
signal based on the differential value of the differentiator in a signal processing
unit;
an offset removal step of removing offset of the input signal using the signal component
analysis value of the signal processing unit in offset removal; and
an integrating step of integrating the input signal in an integrating unit to output
a pressure input signal value from which a heat input signal value is removed.
20. The pressure signal detection method according to claim 19, further comprising a filter
step of removing noise of the input signal in a filter unit so as to remove noise
from the input signal supplied in the signal input step.
21. The pressure signal detection method according to claim 19, wherein in the signal
processing step, the differentiated input signal value is compared with a preset threshold
value to determine whether the input signal is a pressure input signal or a heat input
signal.
22. The pressure signal detection method according to claim 21, wherein:
when the differentiated input signal value is equal to or larger than the predetermined
threshold value, the input signal is determined to be a pressure input signal, and
the integrating step is executed; and
when the differentiated input signal value is smaller than the predetermined threshold
value, the input signal is determined to be a heat input signal, and the offset removal
step is executed.
23. The pressure signal detection method according to claim 19, wherein in the signal
processing step, a reset signal for initializing the integrating step is output when
a pressure input signal during a reference time is not re-detected after a pressure
input signal is detected from the differentiated input signal value.
24. The pressure signal detection method according to claim 19, wherein in the signal
processing step, a reset signal for initializing the integrating step is output when
a pressure input signal is not detected from the differentiated input signal value
in all sections.
25. The pressure signal detection method according to claim 19, wherein
in the offset removal step, a precise pressure value that is obtained by subtracting
the heat input signal and a noise signal from the input signal is output.
26. The pressure signal detection method according to any one of claims 15 to 25, wherein
the piezoelectric material is a piezoelectric film.